Thermoplastic polymers made from a variety of monomers having carboxylic acid groups have been prepared and crosslinked via the carboxylic acid sites by means of a cation, e.g., a monovalent or polyvalent metal. Typically, the polymers are the polymerization product of an olefin, e.g., ethylene or propylene, and an unsaturated carboxylic acid, e.g., acrylic or methacrylic acid. These polymers then are crosslinked with a polyvalent metal, e.g., zinc, or effectively crosslinked with a monovalent metal, e.g., sodium. Such polymers have been used widely for the manufacture of shaped and molded articles, e.g., bottles, for the containment of aqueous mixtures or solutions, e.g., detergents, mouthwash, shampoo, and soap. One of the undesirable features of shaped articles made from these polymers is that the articles have a tendency to collapse when stored for an extended period of time, e.g., 3-9 months. The apparent collapsing of the shaped articles is caused by the escape of vapor or moisture from the container. Another undesirable feature of the article, although along the same line as the previous, is that the product often was degraded due to oxygen contamination.